Biomass steam gasification in fluidized bed of inert or catalytic particles: Comparison between experimental results and thermodynamic equilibrium predictions

In order to improve the understanding of biomass gasification in a bed fluidized by steam, the thermochemical equilibrium of the reactive system was studied. The equilibrium results were compared to LGC experimental results, obtained by the gasification of oak and fir in a laboratory-scale fluidized bed of different catalysts: sand, alumina, and alumina impregnated with nickel. The research was completed by a study of the influence on the equilibrium of additional parameters such as the quantity of steam, the pressure or the kind of biomass. Those results of simulation may be used for evaluating the limits of actual reactors.The following conclusion may be drawn from all the results: The thermodynamic equilibrium state calculated is far away from the experimental results obtained on sand particles. The steam to biomass ratio, between 0.4 and 1 kgsteam/kgdry biomass, has a strong influence on the gas mixture composition. The temperature increase and the use of catalyst allow producing a gas mixture with a high content of hydrogen and carbon monoxide. The H2:CO ratio may reach values greater than 3. The use of catalyst allows the system to get closer from the equilibrium, especially for the nickel based catalyst

Hydrodynamic and solid residence time distribution in a circulating fluidized bed: experimental and 3D computational study

Vertical profiles of local pressure, horizontal profiles of net vertical solid mass flux, and residence time distributions (RTD) of the solid phase are experimentally assessed in the riser of a small scale cold Circulating Fluidized Bed of 9 m high having a square cross section of 1111 cm. Air (density 1.2 kg/m3, dynamic viscosity 1.8×10-5 Pa.s) and typical FCC particles (density 1400 kg/m3, mean diameter 70 mm) are used. The superficial gas velocity is kept constant at 7 m/s while the solid mass flux ranges from 46 to 133 kg/m2/s. The axial dispersion of the solid phase is found to decrease when increasing the solid mass flux. Simultaneously, 3D transient CFD simulations are performed to conclude on the usability of the eulerian-eulerian approach for the prediction of the solid phase mixing in the riser. The numerical investigation of the solid mixing is deferred until later since the near-wall region where the solid phase downflow and mixing are predominant is not well predicted in spite of well-predicted vertical profiles of pressure

Gas and solid behaviours during defluidisation of Geldart-A particles

Bed collapsing experiments were carried out in a cold-air transparent column 192 mm in diameter and 2 m high. Typical Fluid Catalytic Cracking (FCC) catalyst with a mean particle size of 76 μm and a density of 1400 kg/m3 was used. Both single and double-drainage protocols were tested. The local pressure drop and bed surface collapse height were acquired throughout the bed settling.Typical results were found regarding dense phase voidage of a fluidised bed and the bed surface collapse velocity. In addition, bubble fraction was calculated based on the collapse curve.Experimental results showed that windbox effect is significantly reduced compared to previous works since the volume of air within the windbox was reduced. The comparison of single/double-drainage protocols revealed a new period in the defluidisation of Geldart-A particles concerning gas compressibility. Through the temporal analysis of local pressure drop, the progress of the solid sedimentation front from bottom to top was determined, analysed and modelled

Le "remodelage" des terres en Martinique : modification des propriétés de "ferrisols" et d'andosols cultivés en canne à sucre

Le nivellement des collines pratiqué depuis environ 1970 en Martinique pour faciliter la mécanisation des cultures détermine des transformations physicochimiques des sols. Dans cet article les auteurs comparent les propriétés de sols ferrallitiques et d'andosols, dont les horizons A ont été éliminés par ce traitement, avec celles de témoins non remodelé

Écoformation et éducation relative à l’environnement montagnard : entre territoire, nature et culture

Dans un contexte professionnel d’éducation et de formation liée à l’environnement, comment favoriser la rencontre et le dialogue avec la montagne, avec l’éco (Oïkos = habitat) ? Comment explorer nos relations dialogiques et conscientiser l’écoformation vécue entre culture et nature montagnardes ? Comment la montagne symbolique contribue-t-elle à la construction d’un imaginaire à la fois individuel et social, source d’écoformation et base d’éducation relative à l’environnement (ErE) ? Ce questionnement sous-tend un grand nombre de préoccupations tant pédagogiques et environnementales que de développement de territoires montagnards. Une démarche de praticien-chercheur en formation apporte des éléments de réflexion à ce questionnement. Ceci permet de mettre en lumière des processus d’écoformation montagnarde entre nature et culture et souligne la pertinence de méthodes pédagogiques pour une ErE ancrée dans les cultures et territoires de montagne. Au regard des éléments ressortant de cette recherche, nous proposons l’accompagnement d’une écoformation et éducation montagnarde dans des démarches de rencontre transculturelle, pour nous enrichir de la diversité des façons de voir et de vivre le monde à travers la grande richesse de ses cultures et de ses territoires que nous devons préserver et valoriser.Within a professional context of environmental education and training, how can interacting and dialoguing with the mountain, with the eco (Oïkos = habitat) be promoted ? How can we explore our dialogic relationships and make eco-education experienced through mountain culture and mountain nature a conscious process ? How does the mountain as a symbolic entity contribute to build an individual and social imaginary frame, a resource for eco-education and a basis of environmental education ? These questions underlie many pedagogical and environmental concerns, as well as concerns related to the development of mountain areas. An in-training practitioner-researcher approach feeds the questioning process on theses concerns. It enlightens eco-education processes between mountain nature and culture and emphasizes the relevance of pedagogical methods for an environmental education embedded in mountain cultures and places. Considering the results of this research, we suggest the association of mountain eco-education and education with transcultural meeting approaches, to enrich the diversity of ways of seeing and living the world through the great richness of cultures and places we must preserve and value

d13C pattern of dissolved inorganic carbon in a small granitic catchment: the Strengbach case study (Vosges mountains, France)

The transfers and origins of dissolved inorganic carbon DIC. were studied for a year in a soil–spring–stream system in the Strengbach catchment, Vosges mountains, France. This 80 ha experimental research basin is located on the eastern side of the mountains, at an altitude ranging from 883 to 1146 m.a.s.l. and is mainly covered by spruce 80%.. Brown acid and podzolic soils developed on a granitic basement, and, as a result, the DIC originates solely from CO2 generated by oxidation of soil organic matter. The d13CDIC. in catchment waters is highly variable, from about y22‰ in the springs and piezometers to about y12‰ in the stream at the outlet of the catchment. In the springs, pronounced seasonal variations of d13C exist, with the DIC in isotopic equilibrium with the soil CO that has estimated d13DIC 2 C of about y24‰ in winter and y20‰ in summer. These seasonal variations reflect an isotopic fractionation that seems only induced by molecular diffusion of soil CO2 in summer. In stream water, seasonal variations are small and the relatively heavy DIC y12‰ on average. is a result of isotopic equilibration of the aqueous CO2 with atmospheric CO2